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Structural highlights

Function

[CMR2_PYRFU] CRISPR (clustered regularly interspaced short palindromic repeat), is an adaptive immune system that provides protection against mobile genetic elements (viruses, transposable elements and conjugative plasmids). CRISPR clusters contain sequences complementary to antecedent mobile elements and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA), formerly called psiRNA (prokaryotic silencing) in this organism. Part of the Cmr ribonucleoprotein complex which has divalent cation-dependent endoribonuclease activity specific for ssRNA complementary to the crRNA, generating 5' hydroxy- and 3' phosphate or 2'-3' cyclic phosphate termini. It is not known which subunit has endoribonuclease activity. Cmr complex does not cleave ssDNA complementary to the crRNA. Cleavage of invading RNA is guided by the crRNA; substrate cleavage occurs a fixed distance (14 nt) from the 3' end of the crRNA. In vitro reconstitution shows Cmr1-2 and Cmr5 are not necessary for cleavage. Probably not the subunit that cleaves pre-crRNA, as mutation of numerous metal-binding residues have no effect on cleavage by assembled complex.^[1]

See Also

• Endonuclease

References

1. ↑ Hale CR, Zhao P, Olson S, Duff MO, Graveley BR, Wells L, Terns RM, Terns MP. RNA-guided RNA cleavage by a CRISPR RNA-Cas protein complex. Cell. 2009 Nov 25;139(5):945-56. doi: 10.1016/j.cell.2009.07.040. PMID:19945378 doi:10.1016/j.cell.2009.07.040
2. ↑ Zhu X, Ye K. Crystal structure of Cmr2 suggests a nucleotide cyclase-related enzyme in type III CRISPR-Cas systems. FEBS Lett. 2012 Mar 23;586(6):939-45. doi: 10.1016/j.febslet.2012.02.036. Epub, 2012 Feb 28. PMID:22449983 doi:10.1016/j.febslet.2012.02.036